This invention relates to a novel hardener for hardening gelatin, especially gelatin films of photographic light sensitive materials and a method for hardening gelatin with said hardener.
Generally, photographic light sensitive materials comprise a suitable support such as glass, paper, synthetic resin film, etc. on which are coated various layers such as silver halide emulsion layers, filter layers, interlayers, protective layers, undercoat layers, backcoat layers, ultraviolet absorbing layers, antihalation layers, etc. These constitutive layers comprise the so-called gelatin films mainly composed of gelatin.
Therefore, properties of these constitutive layers depend mainly on properties of gelatin. The properties of gelatin per se such as low melting point, excessive water swelling, low mechanical strength, etc. are fatal defects as properties of constitutive layers of photographic light sensitive materials.
Therefore, hitherto, efforts have been made to improve the properties of gelatin by reacting gelatin with various hardeners to cause crosslinking reactions with functional groups in gelatin molecules such as amino group, carboxyl group, amide group, etc. Many compounds have been known to be effective for hardening gelatin to increase water resistance, heat resistance and scratch resistance of gelatin layers. Examples of these hardeners are aldehyde compounds such as formaldehyde, glutaraldehyde, etc., compounds having reactive halogens as disclosed in U.S. Pat. Nos. 3,288,775, and 2,732,303, British Pat. Nos. 974,723 and 1,167,207, etc., ketone compounds such as diacetyl cyclopentanedione, bis(2-chloroethyl urea), 2-hydroxy-4,6-dichloro-1,3,5-triazine, divinyl sulfone, 5-acetyl-1,3-diacryloylhexahydro-1,3,5-triazine, compounds having reactive olefins as disclosed in U.S. Pat. Nos. 3,635,718 and 3,232,763 and British Pat. No. 994,809, N-methylol compounds as disclosed in U.S. Pat. Nos. 2,732,316, 2,586,168, etc., isocyanates as disclosed in U.S. Pat. No. 3,103,437, aziridine compounds as disclosed in U.S. Pat. Nos. 3,107,280, 2,983,611, etc., acid derivatives as disclosed in U.S. Pat. Nos. 2,725,294, 2,725,295, etc., carbodiimide compounds as disclosed in U.S. Pat. No. 3,100,704, etc., epoxy compounds as disclosed in U.S. Pat. No. 3,091,537, etc., isoxazole compounds as disclosed in U.S. Pat. Nos. 3,321,313, 3,543,292, etc., halogenocarboxyaldehydes such as mucochloric acid, dioxane derivatives such as dihydroxydioxane, dichlorodioxane, etc., inorganic hardeners such as chrome alum, zirconium sulfate, chromium trichloride, etc. However, all of these known hardeners may have any of the following defects when used in photographic light sensitive materials, for example, insufficient hardening action; change of hardening effect with lapse of a long time period called "after-hardening" caused by slow hardening reaction with gelatin; adverse effects on properties of photographic light sensitive materials (especially, increase of fog, reduction of sensitivity, softening of tone, decrease of maximum density, etc.); loss of hardening action caused by other coexisting photographic additives; decrease of effects of other photographic additives (e.g., couplers of color emulsions); formation of stains; difficulty in preparation of the compounds per se in a large amount; poor preservability due to instability of the hardeners per se; etc.
Recently, rapid processing of photographic light sensitive materials has become necessary and improvements for this purpose and improvements of processing solutions suitable for use for such photographic materials have been made. For example, for rapid penetration of processing solution, amount of gelatin in photographic light sensitive materials has been reduced and moreover the layers have been made thin. However, the reduction in the amount of gelatin and making the layers thin cause not only deterioration of film properties, but increase of fog. Thus, because of spread of high temperature and rapid processing by automatic processors and strong processing solutions, films having high mechanical strength and having properties not damaging their photographic characterisics are demanded.